An unusual design in that the butt contains
a removeable magazine powerpack.

Notes

Seen in Star Trek: The
Final Frontier and Star Trek: The Undiscovered Country.
There's no one definitive version of this phaser: in TUC, originals
from TFF were used side-by-side with Ed Miarecki-produced replicas.
Details vary, notably the shape (and design) of the emitter, and of
the magazine butt-plates. This image,
of uncertain origin, shows three different variants; the details, though,
present problems - were there assault phasers on the Enterprise-nil?
Does an Excelsior-class starship need to carry more than 900
hand-weapons, with a crew of only around 500?

Until recently, there was
nothing to indicate, either on the prop or from any official sources
of information, that the Assault Phaser might incorporate a Type-I hand
phaser; the only likely spot was at the rear of the upper body. However,
Andrew Fisher recently sent me this image,
which shows that there is a Type-I located under the barrel housing!
Other pictures of the prop can be found here
and here.

Another unusual setting: a
beam that cuts into the flesh it hits without cauterization, one of
the few times weve seen what these weapons might actually do 
the novelization of ST6 calls them burning phasers
and says theyre outlawed.

There were several other facts
established about phasers in general, but which might only relate to
this model: a stun beam at close range
to the skull can kill; phasers set on wapourise,
as Chekov calls it, set off internal sensors - something he has to be
reminded of by Lieutenant Valeris, which is worrying given he is the
ships Tactical Officer! And - while they weren't too serious about
maintaining continuity of such things throughout the TOS crew's era
- it's worth noting that the beam was blue, as opposed to the usual
yellow-red-orange spectrum of colours.

Liam Kavanagh has recently
turned up the following information from The Making of the Trek Films,
edited by Edward Gross: "William Shatner's hoped for revolutionary
approach to Star Trek V extended to such things as the crew's
hand held weapony, the phasers, which are a far cry from the small plastic
weapons of the earlier films and TV series: big, black and very dangerous
looking, they may well change the look of STAR TREK hardware
to come.

"I didn't want them to be
squirt-guns," said Shatner. "I wanted them to be .45's. We load them
on camera and you can run out of power - you can run out of bullets,
in other words. It makes sense. So we could have a gun, and then not
have a gun. Also, I wanted the phasers to sound differently, too. Instead
of tinkling, I wanted them to crackle."

Laughed Greg Jein, "There
were a lot of things we wanted to build into the new phasers, to make
them more believable as a weapon than a squirtgun. In one scene, a Federation
SWAT team is preparing an assault, and the new phasers give the feeling
of an old war movie. The team actually check their equipment - they
pull the phaser magazine off their bandoliers and if it lights up it's
in working order. Then they slap the magazine into the corrugated steel
butt of the pistol and pull the cocking lever back to expose the mechanisms
to see if its charge is activated, just like the Green Hornet checked
his Hornet's Sting on the '60s TV show. Since the phaser firefight was
shot at night, we put red LEDs in the barels to give the animators a
cue mark for their phaser blasts."

I'm not sure now why this
is called an Assault Phaser; was it me who started it, or did I pick
up on it from someone else? It's a powerful weapon, yes, and one that
could conceivably be carried on a starship in tandem with the TMP-TWOK
phaser that we surmise could have been in service during the same period.
But why, then, have an easily-accessible locker containing FOUR of these
weapons. . . in a kitchen?! Sometimes dramatic licence - the
need for someone to demonstrate what happens when a phaser set to kill
is fired on-board a late-23rd century starship - presents us with a
tricky situation. . .

At one point the final assassination
attempt in TUC was intended to be carried out by a Federation
killer - Colonel West? - using a Starfleet weapon; to this end a sniper-rifle
assembly was built around an assault phaser. In the final shooting script,
though, the assassin was a Klingon (although actually a human in disguise)
using what was presumably a Klingon sniper rifle. An image of what could
be considered the only Type-III phaser rifle from the TOS Movie
era does remain, however.